Telephone system



April 1947- .1. E. OSTLINE 2,419,282

TELEPHONE SYSTEM Filed June 28, 1944 s Sheets-Sheet 1 T0 CONN. BANKS FlG. l CONNECTOR I39 C|O6 -0Z- m LINE LINE FINDER n2 RIZO CIRCUIT SELECTOR REVERS DISTRIBUTER I00 I04 J INVENTOR.

JOHN E. OSTLINE ATTORNE Y5 April 22, 1947.

J. E. OSTLINE TELEPHONE SYSTEM Filed June 28, 1944 3 Sheets-Sheet 2 2 CONNECTOR 231A ffRs TONE k J 232 g 293 BUSY TONE T/ 294 \235 l RING CUT-OFF 2 52 5 271 20 c3 F/ 1 2 0}: 222 lN'tr 2s GEN. R2 v 2se com 203 3 CHANGE I 95 "W OVER P 203J- 2 224 I AVE POLAR TEST R290- SWITCH 262/ R270 c203 HOLD JOHN E. OSTLINE ATTORNEYS Patented Apr. 22, 1947 TELEPHONE SYSTEM' John E. Ostline, Chicago, 111., assignor to Automatic Electric Laboratories, Inc., Chicago, 111., a corporation of Delaware Application June 28, 1944, Serial No. 542,505

17 Claims.

This invention relates in general to telephone systems and, more particularly, to automatic switches used in setting up connections to various individual telephones in the system and also for setting up connections by way of an idle trunk of a group of trunk lines terminatin in private branch exchanges.

In telephone systems wherein private branch exchanges are served by a number of lines extending to each branch exchange, it is the usual practice so to design the final connecting switch of the system that this switch has facilities for making connections to both individual telephone lines and to an idle trunk line of a group of trunk lines terminating at a branch exchange.

Various types of final connectors equipped for giving the above services are in common usage and have proved quite satisfactory; however, it has been found that when the number of trunk lines extending to a private branch exchange, referred to hereinafter as a P. B. X, exceeds the capacity of a. single level of the switch, or when it becomes necessary to increase the number of trunk lines terminating in a P. B. X to a number greater than the number of contacts in a single level of the switch, or if in increasing the number of trunk lines to a P. B. X there are no vacant contacts immediately following the existing group of contacts, problems are presented which may be overcome only with difiiculty and expense in order to give the required service.

The present invention provides a simple, economical and efiicient means for providing for a group of trunk lines extending to a P. B. X, which group of trunk lines may be greater in number than the number of contacts in a given level; it also provides means for adding trunk lines to a group of lines already extending to a P. B. X, which additional lines may be greater in number than the capacity of the level in which the existing group is located; it permits the additional lines to be located adjoining the existing group, allows for a number of individual lines to be placed between the existing group and the added lines, and permits the additional lines to be located on contacts of another level. These results are accomplished with a minimum of op-- erations of the switch and in such a manner that the wiper sets are moved but once across the bank contacts of a group whereby tests are made on contacts of two levels; that is, as the two respective sets of wipers engage the two respective contact sets in the two levels, a test is first made by the first set of wipers and if that contact is found busy or vacant the second set makes a test upon the corresponding contact engaged by the second set of wipers before the switch moves the wipers to the next successive contact.

It is an object of the invention to provide, in a telephone system of the type referred to above, an automatic switch which is adapted to search for an idle line ,over contacts in a plurality of levels simultaneously. Another object i to provide an automatic switch which is adapted to terminate a group of trunk lines connected to a P. B. X Or the like, in which the different lines of the group terminating in the switch bank contacts may be located on a plurality of levels. A further object is to provide an automatic switch adapted to terminate individual subscriber lines and a plurality of groups of trunk lines, said groups of trunk lines extending to one or more P. B. X5 or to other exchanges; wherein said groups may be located upon successive contacts of a plurality of levels or may have individual subscriber lines connected to contacts interspersed with the contacts of the group. It is a still further object of the invention to provide an automatic switch having a plurality of sets of wipers arranged to make contact with bank contacts of a plurality of levels of contacts simultaneously, said switch being adapted first to test the busy condition of a contact in one level and then to test the busy condition of the corresponding contact in another level before the sets of wipers are moved-to the next adjoining sets of contacts. It is a further object of the invention to provide, in an automatic switch, testing means for ascertaining the idle, busy, or vacant condition of the bank contacts engaged by the wiper sets.

Another object of the invention lies in the arrangement of an automatic switch wherein a group of trunk lines terminate on two levels of a switch, and are arranged so that the trunk lines of said group may or may not be connected to successive contacts in the two levels, whereby the switch is arranged to test the contacts in the two levels alternately and to test the contactsas described above, means for giving a busy signal to a calling party in the event all the trunk lines in a group are tested and found busy. A further feature of the invention resides in the arrangement of the rotary connector switch, as

described above, for selecting any particular trunk line in a group of trunks connected to a P. B. X and, if found by test to be busy, a busy tone is caused to be returned to the calling subscriber, and for preventing, on such connectors, automatic rotation of the wipers to search for idle trunk lines in the group. Further objects of the invention relate to the particular arrangement of the circuit elements of the system, whereby the above and other operating advantages of the invention are obtained.

The invention, both as to its organization and method of operation, together with further objects and advantages thereof, will best be understood by reference to the specification taken in connection with the accompanying drawings in which Figures 1, 2 and 3 illustrate the arrangement of a telephone system incorporating a rotary connector embodying the present invention.

Referring to Figs. 1, 2 and 3 of the drawings, there is illustrated therein a telephone system including anexchange serving a plurality of subscriber substations A to E, inclusive, and a P. B. X switchboard 312. More particularly, a plurality of subscriber lines use, 369, 36!, 362 and 3%, respectively, extend to the subscriber substations A, B, C, D and E and terminatein the switching apparatus in the exchange. More specifically, each subscriber line terminates in a line circuit individual thereto included in the switching apparatus, the subscriber line itfi terminating in the line circuit WI and the subscriber lines see, L352 and 363 terminating in similar individual line circuits (not shown). The P. B. X switchboard 312 is accessible to the connector over a group of trunk lines comprising as many as twenty trunks. Also each trunk in the group terminates in the connector bank and includes, in tandem therewith, an individual trunk line circuit illustrated at Sit.

Further, the system comprises a finder-selector link 402' which may be of any known type but which is preferably of a type including Strowger type switches, according to which the finder comprises a wiper mechanism operable in vertical and rotary directions to find and make contact with a calling line. The selector end of the link comprises a Strovrger switch having a wiper mechanism operable in vertical and rotary directions to select andmake connection with the conductors of an idle connector switch. A line circult is provided for each line, such as the line circuit I01 which is used in telephone systems, and which functions to condition a distributor its to select an idle finder-selector link for use of a calling line. The line circuit ii, the finderselector link E2, the distributor Hit and the trunk circuits 370, terminating at the P. B, X switchboard 3H, have not been shown in detail as they are well known to those skilled in the art.

The connector circuit illustrated in detail in Figs. 1, 2 and 3 comprises two sets of wipers mounted upon a wiper shaft (not shown), the lower set of wipers being mounted the distance or five steps or levels below the upper set. With this arrangement, the wipers of the two sets are adapted to engage the contact sets in two levels five steps apart, i. e., for example, when the upper set of wipers is positioned opposite the tenth level, the lower set or wipers is positioned opposite the fifth level or contacts. The connector includes a vertical magnet 266, which steps the wipers in a vertical direction, anda rotary magnet HEB-which steps the wipers in a rotary directicn. A release magnet Ill operates to release the wiper shaft and allows the sets of wipers to be restored to their normal position. There are a number of relays in the connector, as follows: a reverse relay Rliii, a line relay RIZG, a hold relay Hist, a control relay R289, a change relay R228, a ring cutoff relay R239, a delay relay R250, a busy relay R260, a test relay RZ'IQ, a step relay RZiiii, a polarized switch relay R290, and two additional polar relays Reed and R310. The polar relays are designed not to operate when only their lower windings are energized and to remain operated under control of the lower windings after they have been operated over a circuit including their upper windings. There are a number of vertical off-normal springs which operate upon the first vertical step of the switch, including the springs [2%, I25, I25 and 205, and there are also a pair of rotary off-normal springs 2% which are operated upon the first rotary step of the switch. The normal post springs 3E5 are operated upon certain specific levels, which levels terminate groups of trunk lines extending to the P. B. X.

A better understanding of the operation of the system illustrated may be had by describing the progress of a call originating at the substation A and routed through the exchange apparatus to a line terminating at the substation B. The subscriber at substation A by removing the handset of the telephone instrument thereat from its associated switchhook causes a circuit to be completed, whereby the line circuit lDi is operated. The operation of the line circuit mi places starting ground upon the conductor CW3 whereupon the distributor Hi l, in a well known manner, selects an idle finder-selector link, such as the. link m2. for use. When the finder-selector link m2 has been selected, the finder switch there-- of operates in a well known manner to automatically search for and connect with the contacts terminating the line circuit lill of the calling line. At this time the connection has been extended from the substation A by way of the line Hill, the line circuit ldl, and thefinder switch portion of the finder-selector link [-62 to the selector portion of the link. The selector is now conditioned to receive and respond to the first digit to be dialed by the subscriber and accord-- ingly transmits dial tone to indicate to the calling subscriber that the digits of the called subscriber number may be dialed. The selector switch of the link It? operates in response to the dialing of the first digit to elevate its wipers 535 to I37, inclusive, to a position opposite the desired level and then automatically rotates the wipers to select a set of bank contacts terminating an idleconnector, such as the connector illustrated.

Upon seizure of the connector, the control relay R208: is operated over a circuit extending from ground in the finder-selector link use by way of the control wiper I35 engaging the bank contact terminating the control conductorCHifi, the vertical off-normal contacts I25; and the upper winding of relay 3.2% to battery. The relayRZGii is operated over this circuit and opens the contacts 2% in the circuit of the switch relay R299. Also, at this time, the line relay R126 is operated over the loop circuit extending to the subscriber substation A. This circuit may be traced as extending from ground in the finder-selector link I92 by wayof the control wiper 135, the

engaged contact terminating the control conductor CW8, the lower winding of relay R the'contacts l I 4, to the conductor CIO'I; and from battery by way of the upper winding of the line relay RI20, the contacts III, to the conductor CI 06, the conductors CIOB and CIO'I being connected together over a loop circuit including the wiper I36 and I3! of the selector switch which are connected to the Wipers I38 and I 35, respectively, of the finder switch of the link I02, the line circuit IOI, and the conductors of line I extending to the subscriber substation A. Upon operating, the line relay RI20 completes, at its contacts I2I, an obvious circuit for energizing the hold relay RI30. The hold relay RI30, upon energizing, applies, by way of its contacts I3I, ground potential to the control conductor CI08, thereby causing the finder-selector link I52 to be held in its operated position; and it also applies, at its contacts I3I, ground potential to the upper winding of the control relay R200. At its contacts I32, the hold relay RI30 interrupts a point in the incomplete circuit for energizing the release magnet II'I. At its contacts I33, the relay RI30 applies ground potential to the hold conductor C20! which completes a circuit for energizing the lower windings of the switch relay R290 and of the polar relays R3! and R300. Since these relays are of the polar type, they will not operate until their upper windings have also been energized. The connector switch is now ready to receive the second digit to be dialed by the calling subscriber. As was assumed previously, the called line 365 extending to the station B terminates in the tenth level of the switch contact bank. The line conductors C340 of this line'and the control conductor designated C338,

.it is noted, are located in the tenth level and upon the seventh contact. It will be necessary then that the second digit to be dialed be 0. The line relay RI20 will respond to this digit by restoring and reoperating ten times. When it restores the first time, the circuit for energizing the hold relay Ri30 is interrupted at the contacts I2I. However, the hold relay, being of the slowto-release type, remains operated during the entire ten impulses produced by the dialing of this digit.

At its contacts I22, the relay RI20 completes an intermittent circuit for the control relay R200. This circuit may be traced from ground by way of the contacts I33, the contacts I22 and 203, and the lower winding of R200 to battery. The relay R200 is also of the slow-to-release type and remains operated during the entire period of dialing of the digit. At its contacts I23, the relay RI20 completes a circuit for energizing the vertical magnet 240 each time this relay restores. This circuit may be traced from ground by way of the contacts I23, I34, 204 and 226, and the winding of the vertical magnet 240, to battery. The energization of the vertical magnet 240 drives the wiper shaft one step, thereby closing the vertical oil-normal springs I24, I26 and 205 and opening the vertical ofi-normal springs I25. The line relay RI20, in responding to the digit 0, completes the above-traced circuit for the vertical magnet 240 ten times, thereby driving the wipers ten steps in the vertical direction, positioning the wipers 320, 32I, 324 and 325 opposite the tenth level of the associated bank contacts and positioning the wipers 322, 323, 320 and 321 opposite the fifth level of the associated bank contacts. When the wipers 320, 32 I, 324 and 325 are raised to the tenth level, the normal post springs 3I5 are operated into engagement to prepare a test circuit for the test relay R210 and 6 the polar relay R3Ill. nection being described is to be completed to an individual subscriber line, the circuit including the normal-post springs 3I5 is inefiective. At

the termination of the dialing of the second digit,

the line relay is held in its operated position to interrupt, at its contacts I22, the energizing circuit for the lower winding of the control relay R200, thereby allowing the relay R200 to restore since the holding circuit for its upper wind-' ing is now open at vertical off-normal springs I25. Upon restoring, the relay R200 interrupts a further point in its own holding circuit at the contacts 203' and completes, at its contacts 20I, a circuit for energizing the winding of the changeover relay R220, This circuit extends from ground by way of the rotary off-normal springs 206, the contacts 20I, the vertical off-normal contacts 205, and the winding of R220 to battery, thereby causing the relay R220 to be operated to complete, at the contacts 22!, a circuit for energizing the upper winding of R200. This circuit extends from ground by way of the rotary ofinormal springs 206, the contacts 22I, the vertical ofi-normal springs I26, and the upper winding of relay R200 to battery. Upon being energized, the relay R200 opens the initial energizing circuit for the slow-to -release relay R220 at its contacts 20I and it completes, at its contacts 202, a holding circuit for the change-over relay R220, before the latter relay restores, which circuit extends from ground by way of the contacts 222 and'202, the vertical oii normal springs 205 and the winding of R220 to battery. At contacts 228, relay R220 upon energizing opens a point in the previously traced impulsing circuit for the vertical magnet 240 and at its contacts 225 it prepares a point in the impulsing circuit for the rotary magnet 245, At contacts 224, rela R200 upon energizing prepares a further point in the impulsing circuit for the rotary magnet 245. At its contacts 223, the relay R220 also prepares a point in the incomplete circuit for the switch relay R230, and at its contacts 228, relay R220 completes an obvious circuit for energizing the winding of the delay relay R250. The relay R250, in operating, interrupts, at its contacts 252, a circuit for applying interrupted ringing generator to one of the negative wipers 324 or 326.

The connector now is ready to receive the im pulses transmitted as a result of the dialing of the third and final digit to set the wipers upon the contacts terminating the called line. The line relay RI20 now responds to the third digit, which at this time is the digit 7, by restoring seven times, thereby to complete a circuit for energizing the rotary magnet 245 a corresponding number of times. This circuit may be traced from ground by way of the contacts I23, I34, 204 and 225, and the winding of the rotary magnet 245 to battery. The rotary magnet 245 drives the wipers across the contact bank and thereby moves the wipers into engagement with the seventh set of bank contacts, whereupon the wiper 320 engages the contact terminating the conductor C338 and the wipers 324 and 325 enga e the contacts terminating the line conductors C340 of the line 360 extending to the substation B. When the wipers are rotated one step, the rotary offnormal springs 205 were disengaged to interrupt the previously traced circuit for energizing the upper winding of the relay R200, thereby allowing that relay to restore after all of the impulses of the final digit have been sent, this relaybeing held by a circuit including its lower However, since the conmination of the dialing of the final digit, the relay R200 restores to interrupt, at the contacts 202, the circuit for energizing the relay R220 but due to its slow-to-release characteristics relay R220 does not immediately restore. Upon restoring, the relay R200 also completes, at the contacts 203, a test circuit for the upper winding of the switch relay R290, this circuit extending by way of the contacts 223, 305 and 21!, to the wiper 320 which is now engaging the contact terminating the conductor C338. If the called line is busy, ground potential will be found upon the test conductor C338, thereby short-circuiting the upper winding of the relay R290. However, if the called line is idle battery potential will be found upon the test conductor C338, thereby causing the relay R290 to be energized over a circuit including its upper winding,

It will be assumed at this time that the called line is busy and therefore the upper winding of relay R290 is short-circuited in the manner described above. After a short time, the relay R220 restores to open, at its contacts 228, the circuit for energizing the slow-to-release delay relay R250. Before the relay R250 restores, a circuit for energizing the lower winding of the step relay R280 .is completed over a path from the grounded hold conductor C201 by way of contacts 201, 205, 22? and 253 and the lower winding of R280 to battery. The relay R280 thereupon operates and, at its contacts 283, completed a circuit for energizing the upper windings of the relays R280 and R260, causing the relay R200 to operate. This circuit can be traced from the hold conductor C20! through the contacts 293, 3l3, 308, 283, and 210, and the upper windings of the relays R250 and R283 in series to battery. At contacts 251, the delay relay R250 upon restoring also prepares a circuit for transmitting busy tone to the calling line which circuit may be traced from the busy tone conductor by way of the contacts 293, 26E, and 251, the negative conductor C106, the negative wipers of the link I02, over the negative conductor and to the telephone instrument at substation A, in order to indicate to the calling subscriber that called line is busy.

The subscriber at station A is thus notified that the called line is busy and that he should replace the handset of the telephone instrument upon the associated switchhook in order torelease the connection thus far set up. This release of the equipment will be hereinafter described.

Assuming, on the other hand, that the called line 360 of the substation B is idle when the wiper 320 engaged the contact terminating conductor C333, the wiper 320 will encounter negative battery potential thereon thereby energizing the switch relay R290 over a circuit extending from ground, through the upper winding of the relay R290, the contacts 203, 223, 305, and 2H, and the wiper 320 to negative battery on the conductor C333. The relay R230 then operates immediately, due to the energized condition of its lower winding and prepares, at its contacts 292 and 294, a circuit for transmitting ringing current to the called line 350 to signal the called party. As a further result of the operation of relay R290 ground potential is applied, at its contacts 295, to the bank contact terminating the control conductor C338 thereby to mark the called line busy in the banks of the other connectors having access thereto, and, at its contacts 2!, a

path is completed for transmitting ring-back tone to the calling line over a circuit including the contacts 233 and the negative line conductor CW5, to indicate to the calling subscriber at substation A that the called line is being signalled.

It will be recalled that the relay R220 remained operated for a short interval of time, after its energizing circuit was opened by the restoration of relay R200, in order to complete the above traced circuit for relay R290. Subsequently re lay R220 restores to normal and, at contacts 228, it opens the energizing circuit for delay relay R250. Due to the fact that switch relay R290 has energized and opened its contacts 291 the previously traced circuit for operating the step relay R200 and busy relay R260 cannot be completed at this time. Subsequently the slow-torelease delay relay R250 restores to normal and, at contacts 252, it completes a circuit for transmitting ringing current over the conductors C340 of line 330 to signal the subscriber at substation B.

The path for projecting ringing current to signal the substation B may be traced from the battery connected interrupted generator 254, the upper winding of ring cut-off relay R230, contacts 252, 23d, 232 and 30L wiper 224 in engagement with the seventh contact in the tenth level of bank contacts, negative conductor C340 of the line 300, the ringer at substation B, and returning by way of the positive conductor C340 of the line 360, wiper 325, contacts 303, 204 and 324 to ground.

When the called subscriber at substation B responds to the ringing of his bell by removing his handset from the associated telephone instru- I ment, a direct current bridge is closed across the line conductors C340 in the usual manner, whereupon the ring cut-off relay R230 is energized. Upon energizing, relay R230 closes a locking circuit for its lower winding at contacts 235 from the grounded conductor C23? and, at the same time, its contacts 23! and 234 are opened to disconnect ringing current from the line. Also, at the contacts 233, relay R230 interrupts the path for transmitting ring-back tone to the calling station A. The relay R230, upon operating, also closes its contacts 232 and 235 to complete the talking connection between the called substation 13 and the calling substation A. Transmitter current is now supplied to the called substation through the windings oi the reversing relay Rl l3, whereupon relay Rl 10 operates over the called subscribers loop, and reverses the flow of current to the calling substation A in an obvious manner at its contacts Hi to H4, inclusave.

It is noted that upon a call being made to an individual line, such as the one just described, with the control wipers 320 and 32! resting upon the seventh contacts of the tenth level in the upper set of bank contacts and line wipers 324 and 32% resting upon the corresponding contacts inthe lower set of bank contacts, the wiper 32% engages a contact upon which no conductor is terminated and, therefore, no circuit can be completed for operating relays Rlli'i or R3? and that, also, the control wipers 322' and 323 are resting upon the corresponding contacts in the fifth level in the upper bank, but, since the relays R210 and R3l0 are in their restored positions, no effective circuit is completed by these wipers. Finally, since the line wipers 325 and 321 are resting upon the seventh contacts of the fifth C335 and the line -at its contacts ;use in another call.

level in the lower bank, it will be seen that no effective circuit is completed by these wipers, as the contacts 302 and 304 are in disengaged positions.

The control wiper 320 is utilized to test the idle or busy condition of the individual lines terminated in the connector bank and the wipers 32!, 322 and 323 are employed in the testing of the trunk lines in the group of lines extending to the P. B. X 310. the line 36E extending to the substation C, the second digit transmitted by the calling subscriber causes the connector to position the wipers 320, 32!, 32 i and 325 opposite the fifth level of the associated set of bank contacts. digit '1 transmitted by the calling subscriber rotates the wipers mentioned into engagement with the seventh set of bank contacts in the fifth level whereupon control wiper 326 en ages the contact terminating the control conductor ipers 32A and 325 engage the contacts terminating the line 25!. The control wiper 32! is inefiective at this time, as it engages the vacant contact 31"., and the wipers 322, 323, 326 and 321 do not engage contacts in any level because they are rotated below the set of bank contacts and, therefore, are inefiective to cause operation of relays R300 and R350.

Testing the busy condition of the called line 35!, signalling the called line, and completion of the connection to the called line are accomplished in the same manner as has been described above in connection with extension of a call to substation B.

Release of equipment The release of the switch train is under the control of the calling party. To terminate the connection and cause the switches to be restored ,to their normal positions, the calling subscriber replaces the handset upon the telephone instrument whereupon the loop circuit extending to the line relay Rl20 is opened, causing this relay to restore and, at its contacts l2l, to open the circuit to the relay RI 30. The relay R530 restores after a. short interval and thereby interrupts, at its contacts l3l, the application of ground potential to the control conductor C108. The removal of ground potential from the conductor Cl08 causes the link I02 and the line circuit Hi! to be restored to their normal positions. The relay R530, in restoring, also opens, I33, the circuit for applying ground potential to the hold conductor C201, thereby causing the relays R230 and R290 to restore. The relays R230 and R290, in restoring, open the loop circuit to the called station, thereby allowing the reversing relay Ri l0 to restore. Also, the relay R! in restoring, completes, at

, contacts I32, a circuit for energizing the release magnet H1, this circuit extending from ground by way of the contacts I32, vertical off-normal springs !20, contacts H5, and the winding of M1 to battery. The energization of the release magnet H1 causes the wipers to be restored to their normal positions, whereupon the vertical elf-normal springs 520, I25, I26 and 205 are restored to the normal position shown in the drawings, the previously traced circuitfor energizing the release magnet H1 being interrupted when the vertical cit-normal springs 520 are disengaged. At this time the connector switch is completely restored to normal and is available for Thus if a call is made to- The final 10 Call to the P. B. X

Assuming that a call is to be made from the substation A to the P. B. X switchboard 312,

and that the link I02 has been operated in the manner previously described to select the connector illustrated, when the connector is selected relays R200, Rl20 and Rl30 operate, in the order named, to prepare the connector for further operation. The connector is now ready to receive the impulses of th first digit, which is the second digit dialed at the substation A.

Th line relay Rl20 responds to the impulses of the dialed digit by restoring and operating a corresponding number of times. In this case, ten impulses are transmitted, whereupon the wipers 320, 32!, 324 and 325 are raised to a position opposite the tenth level of the associated bank contacts, it being remembered that the wipers 322, 323, 326 and 321 of the lower set are normally five steps below the wipers oi the upper set and are, therefore, positioned opposite the fifth level of the associated bank contactsc A short time after the second digit has been dialed, the control relay R200 restores and completes a circuit, at its contacts 20 l for the changeover relay R220. This circuit may be traced from ground by way of the rotary ofi-normal springs 206, contacts 20I, vertical off-normal springs 205, and the winding of relay R220 to battery. The relay R220 is operated over this circuit and completes a circuit for the upper winding of the control relay R200 which circuit extends from ground by way of the rotary oilnormal springs 206, contacts 22L vertical of!- normal springs I26, and the upper winding of R200 to battery. Upon being energized, the relay R200 opens the initial energizing circuit for the slow-to-release relay R220 at its contacts 20! and it completes, at its contacts 202, a holding circuit for change-over relay R220, before the latter relay restores, extending from ground by way of the contacts 222 and 202, vertical ofi-normal springs 205, and the winding of relay R220 to battery. At its contacts 226, relay R220, upon energizing, opens a point in the previously traced impulsing circuit for the vertical magnet 240 and, at its contacts 225, it prepares a point in the impulsing circuit for the rotary magnet 245.

The operation of the relay R220 also completes, at its contacts 220, an obvious circuit for the delay relay R250 which then operates and, at the contacts 25l, opens a point in the incomplete busy tone circuit. The operation of the relay R250 also opens, at thecontacts 252, a point in the circuit for applying interrupted ringing generator to the called line. When the wipers 320, MI, 324 and 325 of the upper set reach the tenth level, the normal post springs 3|5 are operated into engagement to prepare a test circuit for the test relay R210 and thepolar relay R3 0.

The connector is now in readiness to receive the final digit to be dialed, which, in this case, will be the digit 1. Upon dialing the digit 1, the line relay Rl'20 is restored once and it is then held energized, thereby to transmit, at its contacts 423, one impulse to the rotary magnet 245. The rotary magnet 225 then operates to drive the wipers 320 to 321, inclusive, one step in the rotary direction into engagement with the respective first sets of contacts in the contact banks. When the wipers are rotated one step, the rotary ofi-normal springs 206 disengage each other to interrupt the previously traced circuit for energizing the upp r winding of the relay R200. The

relay R200 shortly thereafter restores to interrupt, at its contacts 202, the circuit for energizing the relay R220, but due to its slow-to-release characteristics relay R220 does not immediately restore. The restoration of relay R200 also com- 'of relay R290, the contacts 20-3, 223, 305 and 21!,

to the wiper 320, which is in engagement with the bank contact terminating conductor C328. The operation of th switch now depends upon the busy or idle condition of the first set of contacts in the banks engaged by the wipers. It will be noted that the first to the sixth, inclusive, and ninth and tenth contacts in the tenth and fifth levels terminate trunk lines extending to the trunk circuits indicated at 316, which connects to the P. B. X switchboard 312 by way of the cable 31!.

Assuming that the trunk line, including line conductors C322 and control conductor C328, terminated by the first contact set in the tenth level in the associated contact bank is the first idle trunk in the associated group of trunks, accordingly when the wipers are rotated into engagement therewith, battery potential upon the control conductor C328, marking the trunk idle, is applied to the wiper 320. The app ication of battery potential to the wiper 320 completes a circuit, including contacts 21!, 305, 223 and 203, for energizing the upper winding of the switch relay R200.

When thus energized the switch relay R290 operates to interrupt, at contacts 291, a point in the circuit of step relay R280 thereby to prevent energization of the latter relay when the slowto-release change-over relay R220 subsequently restores, and to complete, at contacts 295, a circuit, including the contacts 305 and 21!, for applying direct ground potential to the wiper 320 in order to busy the trunk in the associated bank contacts of other connectors having access thereto. The slow-to-release change-over relay R220 now restores and, at its contacts 223,0pens the initial energizing circuit for the upper winding of switch relay R200. However, the latter relay remains in its energized position under control of the circuit including its lower winding. As a further result of the restoration of relay R220, the circuit for the delay relay R250 is opened at contacts 228, whereupon relay R250 restores and prepares, at contacts 252, the circuit for signaling the operator at the P. B. X switchboard 312.

Also, upon operating, the switch relay R290, at its contacts 29L connects the ring-back tone to the calling line by way of contacts 233 and negative line conductor CliJii to indicate to the calling subscriber at substation A that the called trunk line is being signaled, and, at its contacts 292 and 204, relay R200 completes a signaling circuit whereby the interrupted generator 252 and direct ground at contacts 230, respectively, are connected to the trunk line conductors C322 by way of wipers 324 and 325 to signalthe operator at the P. B. X switchboard 322. the operation of the apparatus with respect to ringing, answering, and releasing the connection is similar to that explained above.

It will now be assumed that "when the connector was operated in the above-described manner and the wiper 320 engaged the first contact in the tenth level of the associated set of bank contacts, the first trunk line was busy and, therefore, the control conductor C328 was grounded by From this point,

a control wiper, such as 320, of another connector. Accordingly, when the wiper 320 of the illustrated connector encounters the bank contact terminating the grounded control conductor C320, the switch relay R 220 will not operate due to the fact that the upper winding thereof is short-circuited. The change-over relay R220 restores after a short interval to prepare, at its contacts 222, a circuit for the test relay R210. Upon restoring, relay R220, at its contacts 228, also opens the energizing circuit for the slow-torelease delay relay R250 and it prepares, at its contacts 229, a circuit for energizing relay R250, the lat er circuit being completed responsive to the energization of test relay R210 before the slow-to-release relay R250 restores to normal, as will be subsequently described. Also, upon restoring, the relay R220 completes, at its contacts 221, a circuit for energizing the lower winding of the step relay R280. This circuit may be traced from the grounded hold conductor C201 by way of the contacts 201, 246, 221 and 253, and the lower winding of the relay R280 to battery. The relay R280 then operates to complete a holding circuit for its upper winding in series with the upper winding of the busy relay R200, this circuit extending from the grounded hold conductor C201 by way of the contacts 220, M3, 308, 283 and 218, and the upper windings of the relays R260 and R280 in series to battery. The busy relay R260 is operated over the above-traced circuit and completes, at contacts 202, the test circuit including the upper winding of the test relay R 210. With ground potential applied to the contact terminating the conductor C320, 9, circuit will be completed for the upper winding of the test relay R210, this circuit extending from the grounded conductor C328 and its associated bank contact, wiper 320, the contacts 21!, 305 and 224, the upper winding of R210, the contacts 262 and 215, the normal post springs 3i 5, the wiper 32 I, the bank contact terminating the conductor C320, and the resistor 330, to negative battery. The relay R210 is operated over this circuit and completes, at the contacts 216, a holding circuit for its lower winding, this circuit including the contacts 225 and the grounded holding conductor C201. At this time, when the wipers 320 and 32l have tested the busy condition of the first trunk line in the tenth level, a circuit is prepared at the contacts 213 of the test relay R210 for testing the first trunk line in the fifth level. Assuming that the contacts terminating the first trunk line in'the fifth level are found busy, ground potential will be found on the conductor 033i, thereby grounding the wiper 323 to complete a short circuit for the upper winding of the polar relay R300, this circuit including the contacts 213, 28!, 301,

312 and 291 and the grounded hold conductor- C201. Also, upon operating, the test relay R210 interrupts, at its contacts 2'18, the circuit for energizing in series the upper windings of the relays R250 and R280. The relay R260 is deenergized shortly thereafter, However, the relay R280 remain energized over its lower winding in a circuit which includes the contacts 253, 221, 246 and 291 to the grounded hold conductor C201. It will be noted that the delay relay R250 is held operated over a circuit extending from the grounded hold conductor C201 by way of the contacts 296, 3E3, 300, 210 and 229, and the winding of R250 to battery.

The switch now having tested the first contact sets in the tenth and fifth levels, respectively, and it having been assumed that the trunk rotary magnet 245.

vance the wiper sets to the second contact sets in the contact banks. A circuit is now completed for the rotary magnet 245 by the restoration of relay R260, this circuit extending from the grounded hold conductor C251 by way of the contacts 296, 313, 308, 283, 2'" and 263, and the winding of the magnet 245, to battery. Upon energizing, the rotary magnet M5 drives the wipers to the second contact sets in the banks and also interrupts, at the contacts 245, the circuit for energizing the lower winding of the stepping relay R280. Upon restoring to normal, the relay R280 opens, at contacts 28L the test circuit for the upper winding of polar relay Rti t, and prepares, at contacts 282, a test circuit for the upper winding of polar relay R3), andit opens, at contacts 283, the energizing circuit for the If it be assumed that the third trunk line, which is terminated upon the second contact set in the tenth level, is busy, ground potential will be found upon the control conductor C334 to ground the wipers 320 and 32! whereby the upper winding of the polar relay R310 is short-circuitedover a circuit which may be traced from the grounded wiper 32!, normal post springs SIS, contacts 21%, upper winding of relay R3Ill, contacts 282, 337, 3I2 and 251, to the grounded conductor C281. When the rotary magnet 245 restores to normal a circuit is again completed, at its contacts 246, for energizing the lower winding of the step relay RZBG. Relay R283 now energizes again to open the test circuit for polar relay R3Ic, at contacts 282, and to close the test circuit for polar relay R388, at contacts 28!. Relay R280, at its contacts 2153, again completes a circuit for energizing the rotary magnet 245. If the wiper 323 is in engagement with an idle trunk line, battery potential will be encountered on conductor C335, whereupon relay R3fi0 immediately operates and opens the stepping circuit of the rotary magnet 2 55, at contacts 308, before this magnet has had an opportunity to be sufliciently energized to rotate the wiper sets an additional step. However, if it be assumed that the above trunk line is busy, the wiper 323 encounters ground potential on conductor C335, whereupon the upper winding of relay R30!) is short-circuited, permitting the rotary magnet 245 to completely energize and advance the wiper sets into engagement with the third set of contacts in the banks and to again open, at contacts 246, the energizing circuit for relay R280. It will be seen from the foregoing description of the operation that the contacts in the tenth level are tested for a busy condition and, if found busy, the corresponding contacts in the fifth level are then tested; and if these latter contacts are found. busy, the wipers are moved to the succeeding contacts where the neXt contacts in the tenth level are tested and, if found busy, the corresponding contacts in the fifth level are tested. This interaction of testing contacts in two levels successively continues until an idle line is found.

If, in testing the lines, the connector finds busy the first twelve lines which are terminated upon the first six sets of contacts in the tenth and fifth levels, the wiper sets are driven into contact with the terminals connected to individual lines which are terminated upon the seventh sets of contacts in the tenth and fifth levels of the connector bank. It will have been noted that tests for idle trunk lines are made over the wipers 32! and 323 and that, as a result of these tests, the wipers are caused to be rotated to sueceeding sets of bank contacts when a busy condition is encountered in both levels. However, in the event the wipers are driven into engagement with contacts terminating individual lines, as in the present instance, no potential will be found upon the bank contacts engaged by the wipers 32! and 323, and, as a result, the polar relays R3!!! or R330 will not operate, but the stepping relay R280 will again operate to complete, at the contacts 283, a circuit including con tacts 263, 271, 388, Sit and 295 and the'hold conductor C237, for again energizing the rotary magnet 245, whereby the wiper sets are driven a further step into contact with the succeeding sets of bank contacts. Attention is called to the fact that, because the test relay R2lii is then in its operated position, the test circuit including the test wiper 325i is ineffective for testing individual lines in the tenth level, since the circuit therefor is interrupted at the contacts 27!, and it Will also be noted that the corresponding upper and lower test contacts terminating the individual lines are not connected together and, therefore, the wiper tZl is open circuited and, as a result, the relay R3!!! cannot operate. Attention is also directed to the fact that inasmuch as the test relay R388 is not in its operated position, the test circuit including the test wiper 322 is ineffective for testing individual lines in the fifth level, since the circuit therefor is interrupted at contacts 306, and it will also be noted that the corresponding upper-and lower test contacts terminating the individual lines are not connected together and; therefore, the wiper 323 is open circuited and, as a result, the relay R309 cannot operate. With the above condition prevailing, it will be seen that the wipers will be advanced over the contacts terminating individual lines without testing the idle or busy condition thereof, and will be driven into engagement with the next succeeding sets of bank contacts. In the present case, the eighth set of contacts in the tenth level terminate an individual line and the eighth set of contacts in the fifth level are vacant. In either case, the wipers are caused to be moved to the succeeding contacts as notest potential is found upon the contacts which are engaged by wiper 322i and 323. It should be noted that if a trunk line is terminated on the eighth set of contacts in the fifth level, with the upper and lower test contacts thereof strapped togeth r in the manner illustrated in the drawings, the test wiper 323 will make the abovedescribed test operation to determine the idleor busy condition of that trunk line.

Assuming now that the wiper sets are resting upon the ninth set of contacts in the tenth and fifth levels of the banks, and that the ninth contact in the tenth level has been tested and found busy, the ninth contact in the fifth level is now tested and found to be idle. Negative battery potential applied to the control conductor C353, which marks the associated line as idle, then causes the polar relay R386 to operate over a circuit which may be traced from the grounded hold conductor C201 by way of contacts 297, 3E2, 301,

28L 2T3, the upperwinding of relay R330, and the wiper 323 engaging the bank contact terminating the conductor C353. Due to the pre-energized condition of its lower winding, relay R300 operates exceedingly fast to open, at contacts 388,

the circuit of the rotary magnet 245, beforethe magnet has had sufficient time to completely energize.

amazes As a further result of opening of contacts 328, the holding circuit for the delay relay R250 is opened, whereupon the latter relay slowly restores to normal. Relay R302, upon operating, at its contacts set, also opens the initial energizing circuit for its upper winding. However, the relay now remains in its operated position under control of the circuit, including its lower winding. The relay R392, upon operating, at its contacts 32! and 323, also disconnects the line wipers 322 and 325 which are now engaging the ninth set of contacts in the tenth level of the bank, while, at contacts 322 and 322, it connects the line wipers 325 and '32! which are engaging the contacts terminating the idle trunk line extending to the P. B. X. Also, upon operating, the polar relay R320, at its contacts 3%, opens a point in the test circuit including the wiper 320, and, at the contacts 306, completes an energizing circuit for the upper winding of the switching relay R292, this circuit extending from the negative battery applied to the conductor C353, by way of the bank contact engaged by the wiper 322, the contacts 355, 224, and 212, and the upper winding of the relay R222 to ground.

The switching relay R292 operates over the above traced circuit and opens, at its contacts 29%, the holding circuit for the test relay R2l2, thereby causing that relay to restore, and it opens, at

its contacts 291, a point in the circuit for energizing relay R282. The relay R292, in operating, also places ground potential upon the conductor C353 over a circuit extending by way of the contacts 225 and 326, and the wiper 322, thereby marking the associated trunk line as busy. As a further result of the energization of relay R292 a circuit is prepared, at its contacts 292 and 295, for transmitting ringing current over the selected trunk line and, at its contacts 29!, ring-back tone is transmitted to the calling line to indicate to the subscriber thereat that the operator at the P. B. X is being signaled. When the slow-to-release delay relay R250 completely restores it completes, at its contacts 252, the previously traced circuit for signaling the selected line. The ringing current transmitted over the selected trunk line causes the associated trunk circuit in the group of trunk circuits 370 to operate and signal the operator at the P. B. X board 3'l2 that a call is to be answered.

The operator at the swtichboard 312, in answering the call, causes the associated trunk circuit to complete a loop circuit to the connector, thereby causing the ring cut-off relay R232 to be operated in the manner explained above with respect to answering a call to an individual line. The functions of the connector relative to the conversation period and the release of the connection are the same as described above except that, in the present instance, the relay R302 is operated, so that when the release takes p this relay also restores along with the relay R290 as they are both held over the same circuit.

Further, let it now be assumed that the connector, in searching for an idle line, encounters as the first idle trunk line in the group of trunk lines the trunk terminating upon the set of contacts in the tenth position in the tenth level.

In that event, the test wiper 32H, upon engaging the bank contact of the associated lineycompletes a circuit for energizing the upper winding of the relay RBM over a circuit which may be traced from ground upon conductor C221 by way of the contacts 297, 312, 221, 222, the upper wind- "ing of the relay R3), the contacts 214, the normal post springs 3|5, the wiper 32! and engaged contact, to negative battery potential applied to conductor C352. Due to the pre-energized condition of its lower winding, relay R3!!! operates exceedingly fast to open, at contacts 353, the circuit for the rotary magnet 24-5 and the holding circuit for the slow-to-release delay relay R252. At its contacts 312, the relay R350 also opens the initial energizing circuit for its upper winding. However, relay R3) now remains in its operated position under control of the circuit including its lower winding. In operating, the relay R3; also completes, at its contacts 3! l, a circuit for energizing the switching relay R298, this circuit extending from ground by way of the upper winding of the relay R222, the contacts 272, 22 i, 305 and 3H, and the wiper 322 to negative. battery applied to the control conductor C352. The switching relay R290 operates to perform the functions described above and the operations of the switch are the same with respect to signaling, answering a call and releasing as those heretofore described except that in this case the relay R35!) is held until the ground potential is removed from conductor C227.

The control conductor, such as C354, of the last trunk line in any trunk group is not strapped to the adjacent lower bank contact and the latter bank contact is connected either through a relatively high resistance to battery or through a high resistance winding of a traffic meter to battery. In the event that the connector cannot find an idle trunk line in a group of trunk lines, the wipers thereof come to rest upon the last set of contacts, where either the control wiper 32l in the upper set or the control wiper 323 in the lower set engage the bank contact terminating the resistor or meter which is connected to battery. If the last trunk line in the fifth level, as illustrated, is selected, the resistance in series with the battery operates upon the contact engaged by wiper 323 to cause the relay R329 to operate whether the last trunk line in the group is idle or busy. If, however, the last trunk line of the group terminates in the tenth contact set of the tenth level, then when the wiper 32! en-- counters this last trunk line, battery potential, either through a resistance or through the winding of a trafiic meter, applied to the associated bank contact causes th relay R3) to operate whether the selected last trunk line is idle or busy. The relay R320 or the relay Rdlll, in operating, completes, at either the contacts 389 or 3M, respectively, a circuit for energizing the busy relay R262, this circuit extending over the conductor C2 ill, the contacts 2%, 329 or SM, and 2'i9, and the lower winding of R220 to battery. The relay R259, in operating, completes, at the contacts 25!, the circuit for impressing busy tone upon the calling line in the manner heretofore described with respect to making a call to a busy individual line. However, it is to be noted that the busy tone circuit is completed only in the event that the last trunk line of the groupis also busy and relay R290 is, therefore, short-circuited in the manner previously described. If th last trunk line in the group is idle and it terminates in the tenth level, battery potential is applied to the bank contact engaged by the test wiper 322 and causes switch relay R296 to energize over a previously traced circuit. However, if the last trunk line of the group terminates in the fifth level, then battery potential is applied to the bank contact engaged by the test wiper 322 and causes switch relay R290 to energize over a pre- 1 7 viously traced circuit. Energization of relay R290 prevents the transmission of busy tone to the calling subscriber when the busy relay R260 operates. The switching relay R290, in operating, performs the above described functions including that of connecting ringing current to the selected trunk line to signal the operator at the P. B. X switchboard 312. The meter 350, if used, will operate to record the fact that all the trunk lines of the group have been tested and were found busy or that all the trunk lines of the group except the last trunk line have been tested and found busy. This record may be used to indicate, if it is found that the trunk group is busy an excessive number of times, that a greater number of trunk lines are needed to handle the traific to the P. B. X.

Night service From the foregoing description of operation of the connector it will be understood that whenever the digits Ol are received in the connector the switch functions to raise its wipers to the tenth and fifth levels respectively, and to rotate the wipers into engagement with the first and second trunk lines in the P. B. X group terminating in the first set of contacts in the tenth and fifth levels, respectively. Accordingly, the wipers are automatically rotated over the remaining sets of contacts in these levels in search of an idle trunk line, it being understood that the wipers will continue to rotate over bank contacts terminating individual lines, whether idle or busy, and over vacant bank contacts of the bank'until the last trunk line in the group is tion is completed in the usual manner.

Having described the operation of the connector responsive to the dialing of the digits 01 to search for and select an idle trunk line in a group of trunk lines, a brief description will now be given of the operation which takes place when the calling subscriber desires to establish a connection with a particular one of the trunk lines'in the P. B. X group of trunk lines. This feature is of value for night time service or at any time that certain specific trunk lines are to be called. For the purpose of this description it will be assumed that the connector has been seized by the calling subscriber, that the first digit received by the connector is the digit 0, and that the final digit 3 has been dialed,'indieating that the calling subscriber desires to establish a connection over the third trunk line in the tenth level. The operation of the connector at this time is the same as'when a call is extended to an individual line, i. e., the last digit dialed by the calling subscriber rotates the Wipers directively to the contact set terminating the desired trunk line. It will be noticed that, While the impulses of the last digit are being received to operate the line relay Rl20, this relay, at its contacts I22, intermittently applies ground potential to the lower winding of the relay R200 to maintain the latter relay operated, which in turn maintains, at its contacts 202, the circuit for the relay R220. With the two relays R200 and R220 operated during pulsing, the circuit for operating the rotary magnet 245 is maintained at the contacts 204 and 225. In the event that the desired trunk line is found busy,

and when the wipers 320, 321 324 and 325 engage the associated bank contacts, ground potential, applied to control conductor Ciilti, will be encountered upon the. control contact thereof, the ground potential being conducted by way of the associated control wiper 320 to short the upper winding of the switch relay R290, where-'- upon the busy relay R200 is operated. It will be remembered that the step relay R280 was operated at the termination of pulsing, thereby completing the energizing circuit for the relay R260 from the grounded conductor C207 by way of the contacts 295, 3E3, 308, 233, 218 and the upper windings of the relays R200 and R280. The busy relay R260, in operating, completes, at its contacts 28!, the above-mentioned busy tone circuit extending to the calling telephone to notify the calling party that the desired trunk line is busy and that the call cannot be completed at this time. It should be noted that when a call is extended to a particular trunk line, other than the first trunk in the tenth level, in a group of P. B. X trunks, the test relay R210 is not operated over the circuit, including the wiper 32! and the resistance battery connected by way of conductor C329 to the bank contact engaged by wiper 32E, normally completed when the digits 01 are dialed. Since the test relay R270 cannot operate unless the wiper 32! is rotated to the first contact set in the tenth level, the testing circuit for automatically rotating the Wiper sets to search for an idle trunk line in the group is not completed when a call is extended to a particular trunk line, other than the first trunk, in the P. B. X group of trunks. Consequently the circuits including the test Wipers 322 and 323 are open at contacts 300 and 2'13, respectively. If the called trunk line is found to be idle, negative battery which is encountered upon the control contact by way of the wiper 320, causing the switching relay R290 to operate. The relay R230, in operating, switches the calling line through to the wipers 324 and 325 engaging the third set of bank contacts in the tenth level terminating the desired trunk conductors C316. The remaining operations of the connector including signaling of the called trunk line, conversation over the established connection, and release of the connection upon the termination thereof, are accomplished in the same manner as have been described hereinbefore.

It will now be assumed that the calling subscriber desires to establish a connection with a particular trunk line in the group of P. B. X trunk lines terminating in the fifth level of the associated sets of bank contacts. For the purpose of this description it will be assumed that the connector has been seized by the calling subscriber in the usual manner, that the first digit received by the connector is the digit 5 and that the final digit 1 has been dialed indicating that the calling subscriber desires to establisha connection over the first trunk line in the fifth level. It should be understood that the calling subscriber may also establish a connection with any other trunk line terminating in the fifth level by merely dialing a final digit having a numerical value corresponding to the contact position of the bank terminating the wanted trunk line. The operation of the connector responsive to the receipt of the digits 51 is the same as has been previously described in connection with the call extended to the individual subscriber line 36| extending to substation C. In other words, the Wipers 320, 32!, 324 and 325 are positioned opposite the fifth level by the dialing of the digit 5 a 19 c and are rotated into engagement with the first set of bank contacts in the fifth level when the final digit 1 is dialed. If the control conductor CS3! has ground potential applied thereto, indicating that the associated trunk line is busy, the calling subscriber receives the busy tone signal and releases the connection in the usual manner'. However, if the control conductor CS3! has battery potential applied'thereto, indicating that the associated trunk line is idle, the connection is switched through and signaling takes place in the manner previously described. When the conversation is completed and the subscribers replace the handsets upon the associated hook or cradle of their respective telephone instruments, the

connection is released in the same manner as has been described hereinbeiore.

The arrangement of the group P. B, X trunk lines extending to the trunk circuits 310 need not be confined to the corresponding contact sets in the tenth and fifth levels of the connector bank as is shown in the drawings, and may, for example, be connected to bank contact sets in one level, if ten or less trunks are provided in a grill/1P of P. B. X trunks; or, if it is anticipated that the future growth of P. B. X trunk lines in a group will ultimately exceed ten trunks, it may be advisable to connect five trunks of the group to the first five bank contact sets in the tenth level and the remaining five trunks to the first five bank contact sets in the fifth level. Additional trunks may then be added to any vacant bank contact sets in either the tenth or fifth levels, or to vacant bank contact sets in both levels. It should be understood, however, that it is not essential that corresponding bank contact sets in the tenth and fifth levels terminate trunk lines of the P. B. X group of trunks. As a modification of the conhector illustrated, it may be of some advantage to space the sets of wipers on the wiper shaft a (not shown) one or more step or levels apart in stead of five levels apart as is illustrated. For example, the lower wiper set, comprising wipers 322, 323, 326 and 321 may be spaced one step or level apart from the corresponding upper wiper set comprising wipers 32 6, 321, 324 and 325. With this arrangement, when the upper wiper set is in engagement with the bank contacts in the tenth level, the lower wiper set will be in engagement with corresponding bank contacts in the ninth level, it being understood that with this spacing arrangement of the upper and lower wiper sets the trunk lines of the P. B. X group of trunk lines are to be connected to bank contact sets in the ninth and tenth levels instead of the fifth and tenth levels as is illustrated in the drawings.

While the present invention has been described in relation to a connector switch in a telephone system, it is understood that the invention may be applied to various other switches in other stages of a telephone or switching system and that various modifications may be made therein, and it is intended to cover in the appended claims all such modifications as fall within the true spirit and scope of the invention.

What is claimed is:

1. In a telephone system, an automatic switch comprising a contact bank having contacts arranged in levels, two sets of wipers operable by said switch to make contact simultaneously with the contacts in two of said levels, a group of trunk lines terminated upon contacts in said two levels, aplurality of individual lines terminated upon contacts interspersed with the contacts upon auras which said first-mentioned'lines terminate, and means including said wipers for successively testing the busy condition of said trunk lines of'said two levels.

. 2. In a telephone system including separate lines extending to individual substations and a group of trunk lines extending to anotherexchange, an automatic switch comprising a contact bank terminating said lines, said contacts being arranged in levels, said switch having two sets of wipers adapted to engage simultaneously contacts in two of said levels, means for automatically moving said wipers progressively over said contacts in search of an idle trunk line when a call is made to another exchange and thereby testing the corresponding contacts in the two levels for busy condition alternately, and means for directively moving said wipers to any desired contacts in said bank when a call is made to a substation or to a particular trunk line.

3. In a telephone system, an automatic switch having two sets of wipers, a contact bankhaving contacts arranged in two levels, each level comprising a plurality of similarly arranged contacts, a group of trunk lines divided into two subgroups, the trunk lines of one subgroup terminating upon contacts of one of the said levels and the trunk lines of the other of said subgroups terminating upon contacts of the other of said 1evels, individual lines terminating upon contacts of the said two levels, said contacts terminating said individual lines being commingled among said contacts terminating trunk lines of said group, means for operating said switch to-position one of said sets of wipers into engagement with the contacts of one of said levels terminating the first trunk of said group and simultaneously to posi tion the other of said sets of wipers into engagement with the contacts of the other of said levels, and means in said switch for advancing the wiper sets over the successive contacts in said two levels of trunk lines.

4. In a telephone system, a plurality of trunk lines, an automatic switch comprising a contact bank and a plurality of wipers, said contact bank comprising a plurality of contacts arranged in horizontal levels, certain of said contacts being adapted to be engaged simultaneously by a plurality of said wipers, a plurality of telephone lines, a first set of said contacts terminating a single telephone line, a second set of said contacts being contacts upon which no line terminates, a group of said contacts including contacts in two of said levels of contacts terminating a group of said trunk lines, said first and second sets of said contacts being disposed between said contacts of said group of contacts, means for designating the contacts associated with busy lines as busy and for designating the contacts associated with idle lines as idle, means controlled by said switch for operating said wipers to make contact with said contacts to test the busy or idle condition of each of the associated trunk lines, means for testing the corresponding contacts in said levels sequentially before the wipers are operated by said switch to test the next succe-eding contacts in the group, andmeans in said switch for controlling saidwipers to pass over said first and second sets of contacts regardless of their busy or idle condition.

5. In a telephone system, a selecting switch ranged ma plurality of levels, a group'of trunk lines terminating upon contacts in two of said levels, individual lines terminating upon other contacts in said two levels, two sets of contact wipers included in said selecting switch operable to engage successively the contacts in the said two levels, and means in said switch for establishing connections with trunk lines in said group over either one of said wiper sets and for establishing connections with said individual lines over a particular one of said wiper sets.

6. In a telephone system, a selecting switch comprising a contact bank having'contacts arranged in a plurality of levels, each level including sets of contacts, a group of trunk lines terr'ninating upon some of'the contacts in two of said levels, a first individual line terminating upon a set of contacts in a first level of said two levels, a second individual line terminating upon a set of contacts in asecond level ofsaid two levels, a first and a second set of wipers included in said selecting switch directively controlled and arranged to pass over contacts terminating said trunk lines in said two levels and operative to select the contact set in said first level terminating said first individual line by said first set of wipers, and means controlled in said switch for moving only said first set of wipers over said second level of said two levels of contacts and operative to select the set of contacts in said second level-terminating said second individual line.

'L'In a telephone system, a calling line, a final selecting switch having access to groups of trunk lines and to telephone lines, said switch including a contact bank having a plurality of contacts arranged in levels, a group of trunk lines terminating upon contacts in two of said levels, said trunk lines normally marked as idle, means for individually marking said lines as busy when seized, said switch including a plurality of wiper sets, means in said switch for positioning said wiper sets into engagement with the contacts in said two levels and for selecting an idle trunk line in said group, means for controlling said last-mentioned means thereby to position one of said wiper sets into engagement with the contacts of either one of said levels terminating a particular trunk line in said group, means for seizing the-selected particular trunk line in the event it is idle, and means for transmitting a busy signal in the event said particular trunk is marked busy unless said selected particular trunk is the first trunk in said group.

8., In a telephone system, an automatic switch comprising a contact bank having contacts arranged in levels, two sets of wipers operable by said switch to make contact simultaneously with the contacts in two of said levels, a group of lines terminated upon corresponding contacts in said two levels, means including said wipers for testing the busy condition of lines terminating at corresponding contacts in said two levels alternately, and automatic means for progressively advancing said wipers over the contacts of said levels regardless of the position of said lines in said levels until a contact terminating a nonbusy'line is encountered.

9. In a telephone system, an automatic switch comprising a contact bank having contacts arranged in levels, two sets of wipers operable by said switch to make contact simultaneously with the contacts in two of said levels, a group of lines, certain of said lines terminated at contacts in one of said levels, certain other of said lines terminated at contacts'in the other of said levels,

vacant contacts in both'of said levels interspersed between some of the contacts terminating said lines, means for testing the busy condition of lines in said two'levels, and means for progressively advancing said wipers over busy and vacant contacts of said two levels whether or not said lines terminated at contacts of said levels are in corresponding contact positions of said levels.

10. In a telephone system, a final selecting switch comprising a contact bank, said contact bank including a control section and a line section, each of said sections including a plurality of contacts arranged in levels, said selecting switch having sets of wipers, operative to engage in unison the contacts in a plurality of levels in each section, a group of trunk lines each having control and line conductors terminating upon contacts in a plurality of levels respectively in said control and line sections, a plurality of individual telephone lines each having control and line conductors terminated upon contacts interspersed with the contacts in the levels which terminate said trunk lines, vacant contacts in the levels terminating said trunk lines, means in said switch for positioning said wipers upon the first contacts in said levels terminating said group of trunk lines and for automatically advancing said wipers over contacts associated with busy trunk lines, busy or idle individual telephone iines, and vacant contacts, and means in said switch for causing one of said sets of wipers to selectively engage with contacts associated with an idle trunk line.

11. In a telephone system, a final selecting switch comprising a contact bank, said contact bank including a control section and a line section, each of said sections includin a plurality of contacts arranged in levels, said selectin switch having sets of wipers operative to engage in unison the contacts in a plurality of levels in each section, a group of trunk lines each having control and line conductors terminating upon contacts in a plurality of levels respectively in said control and line sections, a plurality of individual telephone lines each having control and line conductors terminated upon contacts which are intermixed with the contacts in the levels which terminate saidtrunk lines, vacant contacts intermixed with the contacts in the levels terminating said telephone lines and said trunk lines, means in said switch for positioning said sets of wipers upon the first contacts in said levels terminating said group of trunk lines, means for thereafter automatically advancing said sets of wipers over contacts terminatin busy trunk lines, busy or idle individual telephone lines, and vacant contacts, and means in said switch for terminating the automatic advancement of said wiper sets and for causing one of said wiper sets selectively to engage the contacts associated with the first idle trunk line in said group.

12. In a telephone system, a calling line, a final selecting switch having access to groups of trunk lines and to telephone lines, said selecting switch including a contact bank having a plurality of contacts arranged in levels, a group of trunk lines terminating upon some of the contacts in two of said levels, telephone lines terminating upon some of the other contacts in said two levels, vacant contacts in said two levels, said trunk lines and telephone lines normally marked as idle, means for individually marking said lines as busy when seized, said selecting switch including a plurality of wiper sets operative to select the contacts in said two levels, means in'said selecting switch fordirectively positioning 'one'of said wiper sets upon the first contacts of :said levels terminating the first :trunk in said group of trunk lines, means for thereafter automatically advancing said plurality of wiper sets over contacts in said levels terminating busy trunk lines, busy or idle telephone lines, and vacant contacts, and means in said switch controlled when the contacts terminating the last trunkin said group is encountered by one of said Wiper sets and found busy for terminating further advancement of said wiper sets and for transmitting a busy signal to indicate that all of the trunks in said two levels are busy.

13. In a telephone system, a rotary connector switch including two sets of wipers and an associated contact bank, a group of lines accessible to said sets of wipers in two levels of said bank, each line having a regular anda special test contact in said bank, means fordirectively operating said switch to select a particular one of the lines in said group over one set of said wipers, and means in said switch controlled over said regular and said special test-contacts of the selected line and effective to cause said switch to search for an idle line alternately in said two levels only in the event the selected line is the first line of said group.

14. In a telephone system, a switch having two sets of wipers, each set of wipers including a regular and a special test wiper, a group of trunk lines, each line having test contacts accessible to a regular test wiper of one of saidsets of wipers, means for operating said switch to position the first set of said wipers into engagement wtih a first trunk line in said group and for simultaneously positioning the second set of said wipers into engagement with a second trunk line of said group, automatic means in said switch controlled over said regular and special test wipers of the first set of wipers for starting said sets of wipers rotatin in search of an idle line if said first trunk line is found busy, and means controlled over the special test wiper of the second set of wipers for preventing the actual rotation of said sets of wipers in the event said second trunk line in said group is found to be idle.

15. In a rotary connector, two sets of wipers, each set including a test wiper, a test relay for each set of wipers, a step relay, means for operating said switch to position the wipers thereof into engagement with two trunk lines of agroup of trunk lines, means for completing a test circuit including one of said test wipers and one of said test relays thereby 'to test the idle or busy condition of one of said trunk-lines, means for operating said step relay, means, controlled by said step relay for completing a stepping circuit thereby to advance said sets of wipers to search for an idle trunk line in said group, and means controlled by said step relay for disconnecting said test circuit from said first test wiper and for completing a test circuit for said second test wiper and its associated test relay thereby to determine the idle or busy condition of said sec- 24 0nd trunk line before said sets of wipers are ad vanced by said stepping circuit.

16. In a rotary connector, two sets'of wipers, each set including a test wiper,ra test relay for each set of wipers, a switch relay for both sets of wipers, a step relay, means for operating said switch to position the wipers thereof into en'- gagement with two trunk lines of a group of trunk/lines, means for completing a test :circuit including one of said test wipers and one of said test relays thereby to test the idle or busy condition of one of said trunk lines, means for operating said step relay, means controlled by said step relay for completing a stepping circuit thereby to advance said sets of wipers to search for an idle trunk line in said group, means controlled by said step relay for disconnecting said test circuit from said first test wiper and for connecting a test circuit for said second test wiper and its associated test relay thereby to determine the idle or busy condition of said second trunk line before said sets of wipers are advanced by said stepping circuit, and means controlled by said test relays for operating said switch relay thereby to establish a connection including either of said sets of wipers and an idle trunk line in said group.

17. In a telephone system, an automatic switch having a first and a second set of wipers, means for moving said wiper sets simultaneously, a plurality of levels of contacts available to said'first wiper set, certain of said plurality of levels of contacts available to said second wiper set after they have become available to said first wiper set, a group of trunk lines, said trunk lines terminating at certain contacts in at least twoof said levels, certain other of said contacts in said two levels being unwired and commingled with said contacts terminating said trunk lines, means for operating said wiper moving means to directively operate said first wiper set into engagement with the contacts terminating any particular one of said trunk lines in either level, means controlled in the event said first wiper set is directively operated into engagement with the contacts of a level terminating the first trunk line in said group for causing said first and said second wiper sets to sequentially test for an idle trunk line in said levels, and means for automatically advancing said wiper sets over the contacts of said levels in the event said first and said second wiper sets encounter either busy trunk lines or said unwired contacts in said levels. Y

- JOHN E. OSTLINE.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS 

